1. Field of the Invention
The invention relates to a full mold for manufacturing cast pieces by the full mold casting method.
2. Discussion of the Background
Cast pieces made of ferrous or nonferrous metal alloys can be made with so-called full molds. Full molds are molds containing a plastic foam material lost pattern which decomposes with practically no residue. During the adding operation, the plastic foam material lost pattern decomposes, and the molten metal fills the resulting cavity and solidifies there to yield the desired cast piece.
It has been found, particularly in industrial fabrication of full-mold cast pieces of this type, that it is more difficult to obtain uniform quality cast pieces with full mold casting than with ordinary hollow mold casting. Thus, full-mold cast pieces made from iron alloys initially have unexplained defects. These defects are primarily local, and would not be expected to arise under the production conditions employed. For example, with full-mold cast pieces made of cast iron with spherical graphite, defects in the structure of the spherical graphite develop even though the melt contains sufficient magnesium and is low in sulfur (as is metallurgically required). At the loci of these defects, which are local, there is diminished strength and elasticity.
Also, in the case of full-mold cast pieces with vermicular graphite, one finds that at certain locations in the cast pieces the desired form of graphite fails to develop, so that locally only lamellar graphite is present in the grain structure. The result is a diminishing of the desired properties of the material.
Further, in the case of full-mold cast pieces made of cast iron with lamellar graphite, difficultly machinable spots (hard spots) develop at nonpredeterminable locations.
In studies which have been made on full-mold cast pieces made of steel casting alloys, it has been found that these also have multiple locally limited defect locations. Such defects do not arise when the same alloys are cast in ordinary hollow molds. The defect locations involved here show so-called heat-cracks and hardness spots which are different from the kinds of defects found with cast iron alloys.
The first and obvious approach was to look for the source of the defect phenomena in a partial (incomplete) gasification of the mold material, which can lead to so-called "residues" when the technique of full-mold casting is incorrectly carried out. However, it was already known for a fairly long time, that such "residues" are comprised of carbon (carbon black and lustrous carbon), which tends to prevent hard spots rather than create them, at least in the case of graphite-containing cast iron alloys.
Accordingly, there is a strongly felt need in the art of making and using full-molds, and in making cast pieces made of iron alloys for a process and/or mold which would not suffer from the difficulties outlined above.